title: Inclusion of glycerol in forage diets increases methane production in a rumen simulation technique system.
abstract: We hypothesised that the inclusion of glycerol in the forage diets of ruminants would increase the proportion of propionate produced and thereby decrease in vitro CH₄ production. This hypothesis was examined in the present study using a semi-continuous fermentation system (rumen simulation technique) fed a brome hay (8·5 g) and maize silage (1·5 g) diet with increasing concentrations (0, 50, 100 and 150 g/kg DM) of glycerol substituted for maize silage. Glycerol linearly increased total volatile fatty acids production (P<0·001). Acetate production was quadratically affected (P=0·023) and propionate and butyrate production was linearly increased (P<0·001). Glycerol linearly increased (P=0·011) DM disappearance from hay and silage. Crude protein disappearance from hay was not affected (P=0·789), but that from silage was linearly increased (P<0·001) with increasing glycerol concentrations. Neutral-detergent fibre (P=0·040) and acid-detergent fibre (P=0·031) disappearance from hay and silage was linearly increased by glycerol. Total gas production tended to increase linearly (P=0·061) and CH₄ concentration in gas was linearly increased (P<0·001) by glycerol, resulting in a linear increase (P<0·001) in mg CH₄/g DM digested. Our hypothesis was rejected as increasing concentrations of glycerol in a forage diet linearly increased CH₄ production in semi-continuous fermenters, despite the increases in the concentrations of propionate. In conclusion, this apparent discrepancy is due to the more reduced state of glycerol when compared with carbohydrates, which implies that there is no net incorporation of electrons when glycerol is metabolised to propionate.
authors.affiliation: Faculty of Veterinary Science, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Jorge
authors.initials: J
authors.lastname: Avila-Stagno
authors.affiliation: Faculty of Veterinary Science, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Alexandre V
authors.initials: AV
authors.lastname: Chaves
authors.affiliation: Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada T1J 4B1.
authors.forename: Gabriel O
authors.initials: GO
authors.lastname: Ribeiro
authors.affiliation: Centro de Investigación y Desarrollo CIEN Austral CONICYT Regional R10C1002, Puerto Montt, Chile.
authors.forename: Emilio M
authors.initials: EM
authors.lastname: Ungerfeld
authors.affiliation: Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada T1J 4B1.
authors.forename: Tim A
authors.initials: TA
authors.lastname: McAllister
mesh_terms: D000818:Animals; D031724:Bromus / Q000737:chemistry / Q000382:microbiology; D002417:Cattle; D004043:Dietary Fiber / Q000378:metabolism; D004063:Digestion; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005285:Fermentation; D005766:Gastrointestinal Contents / Q000737:chemistry / Q000201:enzymology / Q000382:microbiology; D005990:Glycerol / Q000009:adverse effects / Q000378:metabolism*; D006090:Gram-Negative Bacteria / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D017752:Greenhouse Effect / Q000517:prevention & control; D060434:Herbivory; D008697:Methane / Q000378:metabolism*; D008954:Models, Biological; D012417:Rumen / Q000378:metabolism* / Q000382:microbiology; D012463:Saliva / Q000737:chemistry / Q000201:enzymology; D012820:Silage / Q000032:analysis / Q000382:microbiology; D015854:Up-Regulation; D003313:Zea mays / Q000737:chemistry / Q000382:microbiology
chemical_list: D004043:Dietary Fiber; D005232:Fatty Acids, Volatile; D008697:Methane; D005990:Glycerol